DAS system based on multi-band linear sweep frequency pulse

Abstract

The utility model discloses a DAS system based on multi-band linear sweep frequency pulses, and relates to the technical field of distributed sound wave sensing. The DAS system comprises a narrow linewidth laser, an optical fiber coupler, a phase modulator, an electro-optical modulator, an erbium-doped optical fiber amplifier, an optical fiber circulator, a dense wavelength division multiplexer, a photoelectric balance detector, a data acquisition card, an arbitrary waveform generator, a direct current source and the like. According to the system, the phase modulator is used for modulating constant-amplitude multi-frequency continuous light, the frequency number of light waves is related to the harmonic number of microwave modulation signals, the frequency interval is determined by the fundamental frequency of the microwave modulation signals, and the continuous light frequency can be flexibly modulated by adjusting the microwave modulation signals, and the modulation bandwidth is large; detected beat frequency signals are compressed into single-frequency signals through pulses, phase information of the single-frequency signals is demodulated, vibration signals along the sensing optical fiber can be detected, the spatial resolution of the system depends on the chirp frequency sweeping range, and the spatial resolution is high.

Description

TECHNICAL FIELD

[0001] The utility model relates to distributed acoustic sensing technical field, concretely relates to a kind of DAS systems based on multi-band linear sweep frequency pulse. BACKGROUND

[0002] Distributed acoustic sensing (DAS) technology has the unique advantages of fast measurement speed, high detection sensitivity, but due to the use of high coherence light source in the existing system, affected by interference effect, leading to the position of coherent cancellation Light signal signal-to-noise ratio is very low, the "dead zone" of phase demodulation, demodulation error is larger.

[0003] To suppress the phase demodulation error caused by the "dead zone" of beat frequency signal in DAS system, researchers have proposed a large number of solutions, such as using multi-mode, few-mode and multi-core optical fiber, scattering enhanced point optical fiber as a sensing unit, or using multi-frequency, multi-wavelength, multi-phase pulse modulation multiplexing. In summary, it is meaningful to continue to improve the solution to obtain better sensing performance. SUMMARY

[0004] In view of the above problems, the utility model provides a kind of DAS systems based on multi-band linear sweep frequency pulse to suppress the phase demodulation error caused by the "dead zone" of beat frequency signal in DAS system.

[0005] A kind of DAS systems based on multi-band linear sweep frequency pulse, comprising: narrow line width laser 1, first optical fiber coupler 2, phase modulator 3, electro-optic modulator 4, first erbium-doped fiber amplifier 5, optical fiber circulator 6, second erbium-doped fiber amplifier 7, dense wavelength division multiplexer 8, second optical fiber coupler 9, photoelectric balance detector 10, data acquisition card 11, arbitrary waveform generator 12, DC source 13;

[0006] Wherein, the light signal output end of narrow line width laser 1 is communicated with the light signal input end of first optical fiber coupler 2, the light signal output end of first optical fiber coupler 2 is communicated with the light signal input end of phase modulator 3 and the light signal input end of second optical fiber coupler 9 respectively;

[0007] The light signal output end of phase modulator 3 is communicated with the light signal input end of electro-optic modulator 4, the light signal output end of electro-optic modulator 4 is communicated with the light signal input end of first erbium-doped fiber amplifier 5, the light signal output end of first erbium-doped fiber amplifier 5 is communicated with the one port 6-1 of optical fiber circulator 6, the two port 6-2 of optical fiber circulator 6 is communicated with sensing optical fiber;

[0008] The third port 6-3 of the optical fiber circulator 6 is in communication with an optical signal input end of a second erbium-doped fiber amplifier 7, an optical signal output end of the second erbium-doped fiber amplifier 7 is in communication with an optical signal input end of a dense wavelength division multiplexer 8, and an optical signal output end of the dense wavelength division multiplexer 8 is in communication with an optical signal input end of a second optical fiber coupler 9;

[0009] An optical signal output end of the second optical fiber coupler 9 is in communication with an optical signal input end of an optoelectronic balanced detector 10, and an electrical signal output end of the optoelectronic balanced detector 10 is in communication with a data acquisition card 11.

[0010] A radio frequency output end of an arbitrary waveform generator 12 is in communication with a radio frequency signal input end of the phase modulator 3, a radio frequency signal input end of the electro-optical modulator 4 and a trigger signal input end of the data acquisition card 11, respectively.

[0011] An output end of a direct current source 13 is in communication with a bias voltage input end of the electro-optical modulator 4.

[0012] In one possible implementation, the narrow linewidth laser 1 is a polarization maintaining laser, the output power is 10 mW, the wavelength is 1550.12 nm, and the linewidth is 1 kHz.

[0013] In one possible implementation, the first optical fiber coupler 2 is a 1x2 polarization maintaining coupler, and the splitting ratio is 90:10; and the second optical fiber coupler 9 is a 2x2 coupler, and the splitting ratio is 50:50.

[0014] In one possible implementation, the phase modulator 3 is a polarization maintaining modulator, and the bandwidth is 10 GHz; and the electro-optical modulator 4 is a polarization maintaining modulator, and the bandwidth is 10 GHz and the extinction ratio is 30 dB.

[0015] In one possible implementation, the center transmission wavelength of the dense wavelength division multiplexer 8 is 1550.12 nm, and the 3dB transmission bandwidth is 0.20 nm.

[0016] In one possible implementation, the 3dB working bandwidth of the optoelectronic balanced detector 10 is 5 GHz.

[0017] In one possible implementation, the sampling rate of the data acquisition card 11 is 10 GS / s, and the sampling resolution is 14 bit.

[0018] The beneficial technical effects of the utility model are:

[0019] The utility model provides a kind of DAS system based on multi-band linear sweep frequency pulse, with the following advantages:1) Frequency modulation is flexible: utilize phase modulator to modulate equal amplitude multi-frequency continuous light, the frequency number of light wave is related with the harmonic number of microwave modulation signal, and the frequency interval is determined by the fundamental frequency of microwave modulation signal, so by adjusting microwave modulation signal, flexible modulation to continuous light frequency can be realized, and modulation bandwidth is large;2) Large dynamic range, high spatial resolution: by long chirp pulse light injection sensing optical fiber DAS system, with large dynamic range;The beat frequency signal detected is compressed into single frequency signal, and then the phase information is demodulated, the vibration signal detection along sensing optical fiber is realized, and the spatial resolution of the system depends on chirp sweep range, not on pulse light width, and the spatial resolution is high. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which several embodiments of the present application are illustrated. In the drawings, the same or similar reference numerals are used to denote the same or similar elements throughout the several views of the drawings.

[0021] Figure 1 It is a structure schematic diagram of the DAS system based on multi-band linear sweep frequency pulse of the utility model;

[0022] Figure 2 It is a multi-frequency continuous light schematic diagram modulated by phase modulator in the utility model embodiment;

[0023] Figure 3 It is a multi-band chirp pulse light schematic diagram modulated by phase modulator and electro-optic modulator in the utility model embodiment;

[0024] Figure 4 It is an up and down band chirp modulation schematic diagram of electro-optic modulator in the utility model embodiment;

[0025] Figure 5 It is a narrow pulse result example diagram that chirp pulse light is compressed into sinc function shape in the utility model embodiment;

[0026] Figure 6 It is a result example diagram that beat frequency signal is compressed in the utility model embodiment. DETAILED DESCRIPTION

[0027] The principles and spirits of the present application will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are presented only to enable those skilled in the art to better understand and implement the present application, and do not limit the scope of the present application in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to convey the scope of the present disclosure to those skilled in the art.

[0028] This utility model embodiment proposes a DAS system based on multi-band linear sweep pulses, such as... Figure 1 As shown, the system includes: a narrow linewidth laser 1, a first fiber coupler 2, a phase modulator 3, an electro-optic modulator 4, a first erbium-doped fiber amplifier 5, a fiber optic circulator 6, a second erbium-doped fiber amplifier 7, a dense wavelength division multiplexer 8, a second fiber coupler 9, a photoelectric balanced detector 10, a data acquisition card 11, an arbitrary waveform generator 12, and a DC source 13.

[0029] In this configuration, the optical signal output terminal of the narrow linewidth laser 1 is connected to the optical signal input terminal of the first fiber coupler 2. The optical signal output terminal of the first fiber coupler 2 is simultaneously connected to the optical signal input terminals of the phase modulator 3 and the second fiber coupler 9. The optical signal output terminal of the phase modulator 3 is connected to the optical signal input terminal of the electro-optic modulator 4. The optical signal output terminal of the electro-optic modulator 4 is connected to the optical signal input terminal of the first erbium-doped fiber amplifier 5. The optical signal output terminal of the first erbium-doped fiber amplifier 5 is connected to port 6-1 of the fiber optic circulator 6. Port 6-2 of the fiber optic circulator 6 is connected to the sensing fiber 7. Port 6-3 of the fiber optic circulator 6 is connected to the second erbium-doped fiber amplifier 7. The optical signal input terminal is connected, the optical signal output terminal of the second erbium-doped fiber amplifier 7 is connected to the optical signal input terminal of the dense wavelength division multiplexer 8, the optical signal output terminal of the dense wavelength division multiplexer 8 is connected to the optical signal input terminal of the second fiber coupler 9, the optical signal output terminal of the second fiber coupler 9 is connected to the optical signal input terminal of the photoelectric balance detector 10, the electrical signal output terminal of the photoelectric balance detector 10 is connected to the data acquisition card 11, the RF output terminal of the arbitrary waveform generator 12 is simultaneously connected to the RF signal input terminal of the phase modulator 3, the RF signal input terminal of the electro-optic modulator 4, and the trigger signal input terminal of the data acquisition card 11, respectively; the output terminal of the DC source 13 is connected to the bias voltage input terminal of the electro-optic modulator 4.

[0030] In this embodiment, preferably, the narrow linewidth laser 1 is a polarization-maintaining laser with an output power of 10mW, a wavelength of 1550.12nm, and a linewidth of 1kHz.

[0031] In this embodiment, preferably, the first fiber coupler 2 is a 1×2 polarization-maintaining coupler with a splitting ratio of 90:10; the second fiber coupler 9 is a 2×2 coupler with a splitting ratio of 50:50.

[0032] In this embodiment, preferably, the phase modulator 3 is a polarization-maintaining modulator with a bandwidth of 10 GHz; the electro-optic modulator 4 is a polarization-maintaining modulator with a bandwidth of 10 GHz and an extinction ratio of 30 dB.

[0033] In this embodiment, preferably, the center transmission wavelength of the dense wavelength division multiplexer 8 is 1550.12 nm, and the 3dB transmission bandwidth is 0.20 nm.

[0034] In this embodiment, preferably, the 3dB operating bandwidth of the photoelectric balance detector 10 is 5GHz.

[0035] In this embodiment, preferably, the sampling rate of the data acquisition card 11 is 10GS / s, and the sampling resolution is 14bit.

[0036] In this embodiment, preferably, the working process of a DAS system based on multi-band linear sweep frequency pulse includes:

[0037] The single-frequency continuous light output by the narrow linewidth laser 1 is divided into two paths by the first optical fiber coupler 2; the upper path is the detection light of the DAS system, and the lower path is the reference light of the DAS system; the continuous light in the upper path is modulated into multi-frequency continuous light with equal amplitude by the phase modulator 3, and then is periodically linearly swept to be modulated into multi-sideband chirp pulse light by the electro-optical modulator 4, and then is pre-amplified by the first erbium-doped fiber amplifier 5; the amplified pulse light is injected into the sensing optical fiber through the optical fiber ring 6; the backscattering Rayleigh scattering light signal in the sensing optical fiber is injected into the second erbium-doped fiber amplifier 7 through the optical fiber ring 6 for power pre-amplification, and then the ASE noise is filtered out by the dense wavelength division multiplexer 8, and then the reference light in the lower path is injected into the second optical fiber coupler 9 for coherent frequency mixing; the photoelectric conversion of the frequency mixing result is performed by the photoelectric balance detector 10, and the data acquisition card 11 is used for recording. The arbitrary waveform generator 12 is used for controlling the phase modulator 3 to modulate the continuous light into multi-frequency light with equal amplitude, and is used for controlling the electro-optical modulator 4 to periodically linearly sweep the multi-frequency continuous light to be modulated into multi-sideband chirp pulse light; at the same time, the data acquisition card 11 is used for collecting the frequency mixing signal. The direct current source 13 is used for providing a bias voltage for the electro-optical modulator 4 to suppress the optical carrier frequency.

[0038] The collected multi-band chirp signal is compressed into a plurality of single-frequency signals with different frequencies, and the amplitude size is used as the weight, and the phase information is weighted and averaged, so as to finally realize the suppression of the coherent fading "dead zone" in the DAS system.

[0039] Figure 2 The schematic diagram of the phase modulator 3 modulating the multi-frequency continuous light in the system is shown in the figure. Figure 3 The schematic diagram of the phase modulator 3 and the electro-optical modulator 4 jointly modulating the multi-sideband chirp pulse light is shown in the figure; it can be seen that the modulated multi-frequency continuous light is equal-amplitude multi-sideband light; the modulated multi-sideband chirp pulse light is linearly swept on both sides of each frequency.

[0040] Figure 4The schematic diagram of the up and down sideband chirp modulation of the electro-optical modulator 4 in the system; the down sideband light expands the frequency of the optical signal from low to high, and the up sideband light expands the frequency of the optical signal from high to low.

[0041] Figure 5 The chirp pulse light is compressed into a narrow pulse with a sinc function shape, and at this time, the spatial resolution of the system depends on the main lobe half-width of the sinc function, that is, depends on the frequency range of the chirp pulse light.

[0042] Figure 6 The result of the pulse compression of the beat frequency signal can be seen that the compression result is a single frequency signal.

[0043] The utility model provides a kind of DAS system based on multi-frequency band linear sweep frequency pulse, with following advantages:1) frequency modulation is flexible: utilize phase modulator to modulate equal amplitude multi-frequency continuous light, the frequency number of light wave is related with the harmonic number of microwave modulation signal, and frequency interval is determined by the fundamental frequency of microwave modulation signal, so by adjusting microwave modulation signal, flexible modulation of continuous light frequency can be realized, and modulation bandwidth is large;2) large dynamic range, high spatial resolution: by long chirp pulse light injection sensing optical fiber DAS system, with large dynamic range;Beat frequency signal detected is pulse compressed into single frequency signal, and then its phase information is demodulated, realizes sensing optical fiber along line vibration signal detection, and the spatial resolution of system depends on chirp sweep frequency range, not pulse light width, and spatial resolution is high.

[0044] Although the spirit and principles of the utility model have been described with reference to several specific embodiments, it should be understood that the utility model is not limited to the disclosed specific embodiments, and the division of aspects does not mean that the features in these aspects cannot be combined to benefit, and the division is only for the convenience of expression. The utility model is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the appended claims.

Claims

1. A DAS system based on multi-band linear sweep pulses, characterized in that, The application relates to a narrow-linewidth laser, a first fiber coupler, a phase modulator, an electro-optical modulator, a first erbium-doped fiber amplifier, a fiber ring, a second erbium-doped fiber amplifier, a dense wavelength division multiplexer, a second fiber coupler, a photoelectric balance detector, a data acquisition card, an arbitrary waveform generator and a direct current source. The light signal output end of the narrow-linewidth laser (1) is communicated with the light signal input end of the first fiber coupler (2), and the light signal output ends of the first fiber coupler (2) are respectively communicated with the light signal input end of the phase modulator (3) and the light signal input end of the second fiber coupler (9). The light signal output end of the phase modulator (3) is communicated with the light signal input end of the electro-optical modulator (4), the light signal output end of the electro-optical modulator (4) is communicated with the light signal input end of the first erbium-doped fiber amplifier (5), the light signal output end of the first erbium-doped fiber amplifier (5) is communicated with a No. 1 port (6-1) of the fiber ring (6), and a No. 2 port (6-2) of the fiber ring (6) is communicated with a sensing optical fiber. The No. 3 port (6-3) of the fiber ring (6) is communicated with the light signal input end of the second erbium-doped fiber amplifier (7), the light signal output end of the second erbium-doped fiber amplifier (7) is communicated with the light signal input end of the dense wavelength division multiplexer (8), and the light signal output end of the dense wavelength division multiplexer (8) is communicated with the light signal input end of the second fiber coupler (9). The light signal output end of the second fiber coupler (9) is communicated with the light signal input end of the photoelectric balance detector (10), and the electric signal output end of the photoelectric balance detector (10) is communicated with the data acquisition card (11). The radio frequency output end of the arbitrary waveform generator (12) is respectively communicated with the radio frequency signal input end of the phase modulator (3), the radio frequency signal input end of the electro-optical modulator (4) and the trigger signal input end of the data acquisition card (11). The output end of the direct current source (13) is communicated with the bias voltage input end of the electro-optical modulator (4). The narrow-linewidth laser (1) is a polarization maintaining laser, the output power is 10 mW, the wavelength is 1550.12 nm, and the linewidth is 1 kHz.

2. The DAS system based on multi-band linear sweep pulse of claim 1, wherein, The first fiber coupler (2) is a 1*2 polarization maintaining coupler, and the splitting ratio is 90:10; the second fiber coupler (9) is a 2*2 coupler, and the splitting ratio is 50:

50.

3. The DAS system based on multi-band linear sweep pulse of claim 1, wherein, The phase modulator (3) is a polarization maintaining modulator, and the bandwidth is 10 GHz; the electro-optical modulator (4) is a polarization maintaining modulator, the bandwidth is 10 GHz, and the extinction ratio is 30 dB.

4. The DAS system based on multi-band linear sweep pulse of claim 1, wherein, The center transmission wavelength of the dense wavelength division multiplexer (8) is 1550.12 nm, and the 3dB transmission bandwidth is 0.20 nm.

5. The DAS system based on multi-band linear sweep pulse of claim 1, wherein, The 3dB working bandwidth of the photoelectric balance detector (10) is 5 GHz.

6. The DAS system based on multi-band linear sweep pulse of claim 1, wherein, The sampling rate of the data acquisition card (11) is 10 GS / s, and the sampling resolution is 14 bit.

7. The DAS system based on multi-band linear sweep pulse of claim 1, wherein, ​

Images